I was a little like that. Not every lesson, but every so often. I'd run out of time for what I wanted to do, or something would kick off and I'd lose track of where I was and have to quickly pack the kids up. Unfortunately, this meant that the books weren't collected, the room was left in a mess and I didn't get a chance to get through a plenary.
Here's my warning: I have been bullied for this. If you do this, you may be bullied for this. But do remember that you'll never forget to deliver a plenary again, and the kids will always leave your lesson on time to get to their next lesson.
Introducing... the plenary alarm.
Our lessons run in the following way: 08:45 - 09:00 (Registration), 09:00 - 10:00 (Period 1), 10:00 - 11:00 (Period 2), 11:20 - 12:20 (Period 3), 12:20 - 13:20 (Period 4), 14:00 - 15:00 (Period 5).
If you'll see the screenshot below (a number of them, joined together), I have alarms set for Monday, Tuesday, Wednesday, Thursday and Friday for 08:55 (to wrap up my registration time, but not on a Tuesday as that's assembly!), 09:50, 10:50, 12:10, 13:10 and 14:50 (10 minutes before the end of each lesson).
This allows me to start wrapping up my lesson, getting the kids to finish up their work, go through some answers, set a final problem, play a game and so on. I can deal with any behaviour issues and I can remind the kids about homework. It's a very simple idea, and I hope that my sharing will help someone. The kids know what time it is and are prepared for their last problem and a challenge.
Just remember that when you're working with colleagues during free periods and your alarm goes off, you should be prepared for wise-cracking ones to come out with 'So.. what have you learnt in the last hour?' or 'Let's recap our work during this period...'.